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Red Mordenite with Stilbite: Reading the Label

By Digital Towns Crystals ยท Last reviewed October 8, 2026

Short answer: "red mordenite with stilbite" is a trade label for Indian basalt specimens where tufts of fibrous mordenite, a high-silica zeolite, sit with peach or white stilbite sheaves. Mordenite itself is white, yellowish or pinkish; the strong brick-red color comes from something mixed into the fibers, most likely iron-bearing material, not from the mineral's own chemistry. Treat the name as a description of appearance and association, and buy on condition, color and contrast.

What does the label actually describe?

Break the phrase into its parts. "Mordenite" names a real zeolite species. "Red" is the color of the mass, not a variety recognized by any mineral authority. "With stilbite" means the piece also carries stilbite, the sheaf-forming zeolite that dominates Indian specimen output. Most listings add "from Nashik, Maharashtra", which places the material in the Deccan basalt quarries north of Pune.

What you are looking at on these specimens is usually a cushion, spray or felt of very fine fibers lining part of a cavity, colored rusty red to orange-red, with stilbite crystals grown on top of or beside it. The fibers are too fine to see individually without a loupe. In a photo they read as a velvety red background, which is exactly why the combination sells: peach or white sheaves pop against it.

Nobody runs X-ray diffraction on a $35 specimen. The identification on these labels comes from the look of the material and from the well-known Deccan association, which is reasonable but not proof. A buyer should read "red mordenite" the way a gem buyer reads "Mexican fire agate": a trade name with a sound basis, not a lab report.

What is mordenite as a mineral?

Mordenite is one of the most silica-rich natural zeolites. The IZA Commission on Natural Zeolites calls it a high-silica zeolite with roughly 28 water molecules per unit cell, which corresponds to about 14.2 weight percent water. Its framework is threaded by large twelve-membered ring channels, the feature that makes it valuable to industry.

Property Mordenite
Crystal system Orthorhombic
Typical habit Thin fibers and needles, tufts, cottony masses
Mohs hardness 3 to 4 (IZA); 5 (Webmineral)
Specific gravity about 2.12 to 2.15
Luster Vitreous to silky
Reference colors Colorless, white, yellowish, pinkish
Streak White

According to IZA, single crystals are thin fibers, 0.1 to 10 mm long. That is why mordenite almost never forms a "crystal" a collector would recognize as one. It forms masses of hairs. Hardness figures disagree between references because a fibrous aggregate is nearly impossible to scratch-test cleanly; treat it as soft and easily crushed.

The name is geographic. Webmineral records the type locality as the shore of the Bay of Fundy, 3 to 5 km east of Morden, Kings County, Nova Scotia, and IZA notes that it was described and named by How (1864).

Why is red mordenite red?

Webmineral lists mordenite's colors as colorless, white, yellowish and pinkish. None of those is brick red. When a fibrous zeolite mass turns deep red, the color is coming from something trapped between or coating the fibers. In basalt cavities the usual suspect is iron: the host lava is rich in it, and fine iron oxide or iron-rich clay stains cavity linings red, orange and brown. That explanation fits the look of the Nashik material, but it is an inference from general geology, not a published analysis of these particular specimens.

For a buyer, the practical consequence matters more than the chemistry:

  • The color is stable. Iron-oxide staining does not fade in light the way some dyed or organic colors do.
  • The color sits in a fragile layer. Rubbing red mordenite can leave pigment on fingers and bare patches on the specimen.
  • Even color is better than patchy. A uniform red cushion behind the stilbite is the desirable look; blotchy brown and gray areas lower the price.

How does mordenite form in basalt?

Mordenite needs silica. IZA notes that in lava sequences it is most common in host rocks that are oversaturated with respect to silica, such as tholeiitic basalt, and its common companions are other high-silica zeolites and silica minerals.

The classic field evidence comes from Teigarhorn in eastern Iceland, as summarized by IZA. From sea level to the 300 m elevation mordenite is abundant there, associated with heulandite, stilbite, scolecite and epistilbite. Higher in the lava pile it occurs only with chalcedony, quartz and clay, and above about 750 m the cavities are empty. Depth controlled the temperature, and temperature controlled which zeolites could grow. The same logic applies to the Deccan: the mordenite-and-stilbite cavities record a specific window of burial heating and groundwater chemistry.

In India, mordenite is one of the core cavity minerals. A distribution study of Deccan basalt between Nasik and Pune, summarized by Turnstone Geological Services, found mordenite the third most frequently encountered mineral, after heulandite and stilbite. The Indian pairing has a classic American parallel: Webmineral pictures pink heulandite crystals up to 15 mm in fibrous white mordenite matrix from the Rats Nest claim near Challis, Idaho.

Is mordenite used for anything besides specimens?

Very much so, which surprises most collectors. The U.S. Geological Survey lists mordenite among the most common natural zeolites, and commercial zeolites go into pet litter, animal feed, soil conditioners and wastewater treatment. The IZA datasheet cites an estimated yearly production in Japan of 150,000 tons and similar tonnage from the Ngakuru deposits in New Zealand, all from altered volcanic ash rather than basalt cavities.

Mordenite's large channels also made it a refinery mineral. IZA describes a catalytic dewaxing process developed by the British Petroleum Company in the early seventies that uses a platinum and hydrogen-form mordenite catalyst. Industrial mordenite is mostly synthetic, but the structure was first understood from natural crystals.

How should fibrous mordenite be handled?

This is the one zeolite where handling advice goes beyond "don't drop it". IZA warns that because many mordenite occurrences are fibrous, the handling of such fibrous mordenite minerals may pose health risks similar to those of erionite and asbestos, and recommends precautions against breathing the fibers during mining and processing. A display specimen sitting on a shelf is not a mining operation, but sensible habits cost nothing:

  • Do not brush, blow or scrape the red fibrous areas; dust settles on them and stays there.
  • Wash hands after handling, and keep pieces away from young children and pets.
  • Never cut, grind or tumble mordenite-bearing material.
  • Store each piece in its own box or on a shelf where nothing rubs against it.

The rest of the specimen needs the usual zeolite care: no heat, no ultrasonic cleaner, no soaking. See the apophyllite guide for the companion minerals.

Buying red mordenite with stilbite: what to look for

Good pieces have an even red cushion of mordenite, stilbite sheaves with intact tips sitting on it, and a solid basalt base. Check photos for bald spots in the red layer and for crushed sheaf ends, both signs of rough packing. At the time of writing, the in-stock Nashik pieces below run from about $0.24 to $0.31 per gram, so size, not rarity, drives most of the price difference:

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Mordenite in stock

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Frequently asked questions

Is red mordenite a real mineral?

Mordenite is a real, IMA-recognized zeolite. "Red mordenite" is a trade description of mordenite masses colored red, most likely by iron-bearing material mixed into the fibers. It is not a separate species or an official variety, so the name tells you what the specimen looks like rather than what a lab measured.

Is mordenite safe to keep at home?

As a display specimen, yes, with sensible handling. Mordenite is often fibrous, and the IZA zeolite commission advises avoiding inhalation of the fibers during mining and processing. Do not grind, scrape or brush the fibrous areas, wash hands after handling, and keep pieces out of reach of children and pets.

Can red mordenite get wet?

Avoid it. Water will not dissolve mordenite, but it can loosen the fine fibers, move the red staining around and lift stilbite crystals from a weak base. A light puff of air from a distance is the most cleaning these specimens should get.

Where does red mordenite come from?

Nearly all of it on the market comes from basalt quarries in the Nashik district of Maharashtra, India, part of the Deccan Traps. Mordenite itself occurs worldwide, from its type locality in Nova Scotia to Iceland, Idaho, Japan and New Zealand, but the red-with-stilbite combination is an Indian specialty.

How do I tell the mordenite from the stilbite on my specimen?

The stilbite forms visible crystals: flat blades bundled into peach or white sheaves with a pearly sheen. The mordenite is the fuzzy or velvety red layer underneath, made of fibers too fine to separate by eye. Under a 10x loupe the mordenite looks like matted hair.

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